1. Field of the Invention
The invention is related to digital fuel control systems for internal combustion engines and in particular to a digital fuel control system for small engines in which the engine's fuel requirements are determined from the fluctuations of the air pressure in the engine's air intake manifold.
2. Description of the Prior Art
In electronically controlled fuel injection systems, the quantity of fuel being delivered to the engine is computed as a function of the quantity of air being inhaled. Most of the fuel control systems currently being used in the automotive industry compute the quantity of air being inhaled by the engine from the engine's speed and the pressure of the air in the air intake manifold of the engine. Typical examples of such fuel control systems are taught by Sarto, U.S. Pat. No. 2,863,433, Taplin et al, U.S. Pat. No. 3,789,816, as well as Graessley, U.S. Pat. No. 4,261,314.
In a similar manner, Bianchi et al, U.S. Pat. No. 4,172,433, teaches a fuel control system in which the fuel quantity is determined from the engine speed and the position of the throttle blade in the throttle body.
In contrast to the prior art described above, Eckert, U.S. Pat. No. 3,931,802, discloses an electronic fuel control system which directly measures the air flow rate through the engine's air intake manifold and does not require an independent measurement of the engine's speed to determine the quantity of fuel to be delivered to the engine.
The disclosed digital fuel control system is different from the fuel control systems taught by the prior art discussed above. Like the Eckert patent, the disclosed digital fuel control system uses a single sensor to measure the quantity of air being inhaled by the engine. As shall be described herein, the output of the engine's sensor provides the information necessary to determine the speed of a small engine and the average air pressure in the air intake manifold of the engine.